1. Field of the Disclosure
The present invention relates generally to clothes washing machines, and more particularly, to a method and system for detecting and quantifying an unbalance mass in a washing machine drum.
2. Description of Related Art
Residential and commercial clothes washing machines are well known. A generally cylindrical drum or basket for holding the clothing and other articles to be washed is rotatably mounted within a cabinet. Typically, an electric motor drives the drum. During a wash cycle, water and detergent or soap are forced through the clothes to wash them. The detergent is rinsed from the clothes, then during one or more spin cycles the water is extracted from the clothes by spinning the drum.
One way of categorizing washing machines is by the orientation of the washing machine drum. Vertical-axis washing machines have the drum situated to spin about a vertical axis. Articles to be washed are loaded into the drum through a door, which is usually situated on the top of the washing machine. A vertical-axis washing machine drum includes an agitator situated therein, which cleans clothes by pushing and pulling them down into the water. A motor typically drives the agitator, in addition to spinning the vertically-oriented drum during spin cycles. The motor usually operates at a constant speed, and a series of gears or belts are configured to drive the proper component at the proper time during each washing machine cycle.
Horizontal-axis washing machines, having the drum oriented to spin about an essentially horizontal axis, do not include an agitator, and a variable-speed motor drives the drum. During wash cycles, the drum of the horizontal-axis washing machines rotates at a relatively low speed. The rotation speed of the drum is such that clothes are lifted up out of the water, using baffles distributed about the drum, then dropped back into the water as the drum revolves.
Both vertical and horizontal-axis washing machines extract water from clothes by spinning the drum, such that centrifugal force extracts water from the clothes. It is desirable to spin the drum at a high speed and extract the maximum amount of water from the clothes in the shortest possible time. Spin time is reduced, but more power is required to spin at a higher speed. The distribution of the clothes about the periphery of the drum affects the washing machine's ability to spin the drum at a high speed.
If the clothes in the drum are not distributed evenly, the drum will not be able to rotate at an acceptable spin speed without excessive drum vibration in the cabinet. Several factors contribute to drum load unbalance problems. For instance, with vertical-axis washing machines, when a wash or rinse cycle completes and the water is drained from the drum, the clothes are gathered at the bottom of the drum, and are not evenly distributed about the entire drum. Moreover, the drum typically is not perfectly cylindrical; but rather, includes a draft. When the drum spins, the clothes will “creep” up the sides of the drum. However, since a constant speed motor typically drives the vertically-oriented drum, the motor quickly ramps the drum up to the full spin speed. There is little chance for the clothes to distribute about the periphery of the drum, so they creep up the drum's sides in an unbalanced fashion.
The unbalanced, spinning drum vibrates within the cabinet. In conventional vertical-axis washing machines, if the vibration is too severe, the drum will trip a switch mounted inside the cabinet, stopping the drum's rotation and activating a drum-unbalance alarm. A user then manually redistributes the wet clothes within the drum, and restarts the spin cycle.
As discussed above, the drum in a horizontal-axis machine is driven by a variable speed motor. This allows the inclusion of a “distribution” cycle, wherein the drum is rotated faster than the rotation speed of a wash cycle, but slower than in a spin cycle. The drum rotation speed is gradually increased, until the clothes begin to “stick” to the sides of the drum due to centrifugal force. The slower rotation speed allows the clothes to more evenly distribute about the sides of the drum. Once the clothes have been distributed about the drum, the speed is increased to a full spin speed to extract the water from the clothes.
Horizontal-axis washing machines, however, are not immune to drum unbalance problems. If the clothes do not evenly distribute during the distribution cycle, the unbalanced load within the drum will cause unwanted vibrations as the drum rotates. Rather than applying all of the motor's power to spinning the drum at the highest possible speed, power is wasted in drum movement and cabinet vibrations. Detecting the amount of load unbalance allows the spin speed to be optimized to give an efficient wash, while at the same time minimizing the vibrations caused by centrifugal unbalance forces. In cases where the amount of unbalance detected is very high, the washing machine can be programmed to stop its spin cycle, shake the drum to redistribute the washing, and then restart the spin cycle.
Thus, it is desirable to detect the presence and the amount of an unbalance condition in a rotating drum to optimize spin speed and/or take corrective action when necessary. However, prior art methods for detecting unbalance conditions have been largely unsatisfactory. The present invention addresses these, and other, shortcomings associated with the prior art.